Hills mountains are all worn flat eventually it takes many thousands of years, but the combined attackednof the weather, chemicals in rainwater, running warlter, wind, glaciers and various other "agents erosion" will wear them flatter and flatter. Valley will get broader, hilltops will gwt lower ridges will narrowe until at las an entire kountain range is turnwd into a lowland plain.
img source: https://en.wikipedia.org/wiki/Weathering
